Our long-range goal is to elucidate the epigenetic control mechanisms of differentiated functions in cultured cells. We have shown that the cytoplasts of non-erythroid cells, upon fusion with Friend mouse erythroleukemia (MEL) cells result in cybrids whose ability to undergo hemoglobin induction by DMSO has been extinguished. We have also shown that cybrids formed between rat hepatoma cytoplasts and Friend cells apparently result in the activation of the dormant phenylalanine hydroxylase (PH) gene of MEL cells. The cytoplasmically acquired phenotypes of the recipient cells are maintained on continuous culture. These findings suggest that positively and negatively acting, cytoplasmic regulatory elements do exist. Our general objective is to establish firmly through cybridization, the existence of such cytoplasmic regulatory elements. Our main objectives are: a. To establish unequivocally the PH expressed in MEL cybrids is due to true activation of the dormant PH gene of the recipient cells. b. To construct "second generation" cybrids in order to distinguish between a "single hit" vs. "continuous action" regulatory mechanism in the epigenetic control of differentiated function. c. To examine coordinate vs. independent control of functions related to hemoglobin induction and the phynylalanine hydroxylating system in the approropriate MEL cybrids. d. To investigate the various parameters of the cell properties that influence cytoplasmic extinction of of hemoglobin introduction and organization of globin gene. f. To investigate the nature of the cytoplasmic regulatory molecules.